1. Field of the Invention
The present invention relates to image processing for image measurement/recognition and image generation, and particularly relates to a technology for generating information densified images of which information contents are greater than those of the original images.
2. Description of the Related Art
In recent years, digitalization of various kinds of image processing equipment, video equipment, and the like, and widespread use of Internet lead to interconnection of computers and household electrical appliances, so that generally-called ubiquitous network society employing remote control, media merger, and the like has been being organized. The Specs of image equipment are wide-ranged due to difference in mechanism, portability, function, and the like, and therefore, image information in various formats is distributed. In a one-segment terrestrial digital broadcast for mobile phones, for example, down-conversion of an HDTV (High Definition Television) image of 1920 pixels×1080 lines to an image of, for example, 320 pixels×240 lines is required for display on the display of a mobile phone. In short, the spatial resolution must be converted according to the spec of image equipment. Further, there may be the case where time resolution in which difference is caused due to difference in refresh rate may be converted in addition to the spatial resolution. For example, a telecine process for converting a movie film format of 24 frames per second into a video format of 30 frames per second is raised as one example.
In resolution conversion, generation of data of which resolution is greater than that at sampling is called “super-resolution.” For example, displaying an image recorded in DV format (576 pixels×480 lines) as an HDTV image requires super-resolution processing for increasing the pixels about two times and the lines about 2.5 times. Also, a high-resolution script is needed for printing. For example, printing on A4 paper (297 mm×210 mm) at a resolution of 600 dpi requires preparation of a script of 7128 pixels×5040 lines. Almost of all cameras have a resolution lower than it, and accordingly, the super-resolution processing is essential in, for example, direct printing from a digital still camera to a printer. The aforementioned two examples use pixel count and line count for representing the resolution and is defined as “space-domain super-resolution.” On the other hand, there may be a case requiring “time-domain super-resolution” for increasing time resolution to be higher than that at sampling. For example, displaying an image recorded by a branch scanning (interlace) method on a display by sequential scanning (progressive) method requires time-domain super-resolution processing for increasing the time resolution two times. Such processing is used in various cases such as a case for using analog broadcast material in digital broadcast.
Such super-resolution processing is regarded as interpolation for generating new data from existing data. The principal conception of the interpolation is estimation of new data from existing data present in the vicinity of the new data. In the space-domain super-resolution, signal values of new data are estimated from signal values of pixels horizontally, perpendicularly, or obliquely adjacent thereto. In the time-domain super-resolution, new data is estimated from immediately preceding data and next data. As specific methods for the space-domain super-resolution, a nearest neighbor interpolation, a bi-linear interpolation, bi-cubic interpolation, and the like are generally known (Non-patent Document 1: “Clarify Three-dimensional Computer Graphics,” Sinji Araya, published by Kyoritsu Shuppan, Sep. 25, 2003, pp. 144–145). Further, there has been proposed compensation for quality degradation, which is due to blur in these interpolation methods, by supplementing high frequency component (Patent Document 1: Japanese Patent Application Laid Open Publication No. 2003-018398A (FIG. 2)).
On the other hand, there has been proposed a method for realizing super-resolution processing in a manner that much low-resolution data are collected so as to include an overlapping region and the corresponding points are connected (Patent Document 2: Japanese Patent Application Laid Open Publication No. 10-069537A (FIG. 2)).